| 摘要 |
A bipolar transistor logic circuit comprises an input terminal for receiving digital logic signals, an output terminal, an output driver including a current sink transistor and a current source transistor, and a control stage coupled between the input terminal and the output driver. When the control stage is nonconducting, the current source transistor is turned ON and the current sink transistor is turned OFF providing a first digital logic signal at the output terminal. When the control stage is conducting, the current source transistor is initially turned OFF and the current sink transistor is turned ON providing a second digital logic signal at the output terminal. If the output load does not provide the amount of current required by the current sink transistor, the current source transistor is turned ON by the control stage and provides the current sink transistor with collector current to prevent the sink transistor from saturating. In an embodiment providing a tri-state output capability, a second input terminal for receiving digital logic signals is coupled to the aforementioned control stage and to a second control stage. When both control stages are conducting, both the current source transistor and the current sink transistor are turned OFF. As a result, the output terminal is set to a high impedance state and neither provides current to nor withdraws from the output load.
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